In a conventional motorized toothbrush of the multi-head type, a disposable brush tip is detachably secured to the handle of the toothbrush. The tip has a plurality of brush heads, which oscillate (as by rotation) under the power of the motor. Each brush head has a plurality of tufts of bristles.
Existing motorized toothbrushes have relatively small “coverage”, i.e. they do not clean large surface areas at one time. This is because the brush heads are relatively small. If they are made too large, they will put an excessive load on the motor as well as cause irritation to the soft tissue of the mouth.
Furthermore, some users operate such toothbrushes improperly. Instead of applying only light pressure, they force the bristles hard against the teeth. Under such conditions, the distal end of each tuft of bristles stays in the same place and the tufts twist themselves tightly in alternate directions. This makes the brushing less effective, because the bristles do not scrub the surfaces of the teeth.
It would be advantageous to provide a multi-head motorized toothbrush tip that would have greater coverage than conventional toothbrushes. It would be advantageous to provide a multi-head toothbrush tip whereby the cleaning member, i.e. the tufts of bristles and/or rubber-like extensions, extending from the brush heads are arranged in a pattern so as to cover a larger area than the brush head itself.
It would also be advantageous to provide a multi-head motorized toothbrush tip that would perform better even when the user applies excessive pressure against the tooth surfaces to be cleaned.
In accordance with the invention, a brush tip for a motorized toothbrush has a first brush head and a second brush head. The second brush head surrounds the first brush head, and the first and second brush heads rotate around different axes in response to motion produced by the toothbrush motor. Means are provided for counter-rotating and accelerating the first and second brush heads either at equal or different angular speeds.
Because the second brush head surrounds the first brush head, the two heads together have a relatively large area and, therefore, greater coverage. And, because the two brush heads counter-rotate at different axes, their bristles do not twist themselves together even when pressed hard against the teeth.
In preferred embodiments, the first and second brush heads are accelerated in opposite directions, the first brush head is circular, and the second brush head is elliptical. The elliptical brush head provides greater coverage than a circular brush head and the opposite motions and rotation at different axes of the heads make it impossible for the bristles attached to the first brush head to twist into the bristles attached to the second brush head. Further, the first and second brush heads may be both circular with the bristles or tufts of bristles on the brush heads being positioned in a splayed manner such that it is impossible for the bristles on the first and second brush heads to twist into each other.
For toothbrushes of the type wherein the motor produces oscillating rotational motion of a shaft, a gear is mounted at the end of the shaft and is used to rotate the brush heads. For toothbrushes of the type wherein the motor produces reciprocating linear motion of an actuator, two connecting rods are used to convert this linear motion into oscillating rotational motion of the brush heads. However, most motorized toothbrushes generally use a battery-powered DC motor as a source of mechanical energy. This mechanical energy takes the form of a one-way rotation of a shaft that is mechanically coupled to the rotor of the DC motor. Therefore, for the above-discussed mechanisms to be usable, the motorized toothbrush must include a motion conversion mechanism that converts the one-way shaft rotation produced by the DC motor into linear reciprocation or into rotational oscillation. This increases cost of manufacture, diminishes power available to the toothbrush heads, and increases noise of the toothbrush during use.
Commonly-owned U.S. Pat. No. 6,349,442 discloses different head rotation mechanisms, each designed for use with a particular type of motorized toothbrush. One mechanism is designed for use with a motorized toothbrush wherein an actuator, such as a plunger, is linearly reciprocated. The other mechanism is designed for use with a motorized toothbrush wherein a shaft is rotationally oscillated.
Commonly-owned U.S. Pat. No. 6,751,823 discloses a motorized toothbrush wherein one-way rotation of a shaft can be used as the mechanical input to drive two counter-rotating heads that rotate about a common axis to prevent the bristles from twisting together.
Other prior art toothbrush tips are disclosed in U.S. Pat. Nos. 5,416,942, 5,850,655, 5,974,613, 6,665,901, 6,957,468, 7,146,675, and 7,392,562.
The present invention discloses an improved motorized toothbrush that has two nesting brush heads that counter-rotate around different axes and driven by either a one-way rotational or oscillating rotational shaft. The two nesting brush heads may rotate and accelerate at the same or different angular speeds.